During various refining operations petroleum feedstocks are often subjected to high temperatures in order to induce the desired reactions to take place. A side effect of the use of these high temperatures is, however, the formation of coke and this is often undesirable not only because it reduces yield but also because it may have other unfavorable effects upon the course of the process. For example, in fluid catalytic cracking (FCC) operations, the accummulation of coke on the cracking catalysts reduces the activity and selectivity of the catalyst and to overcome this, the catalyst must be cyclically regenerated by burning off the coke. Similar effects may occur in other, non-catalytic refining operations such as visbreaking and thermal cracking where the purpose of the process is to maximize the yield of liquid product and minimize the amount of coke produced, even though a certain amount of coke production has generally been regarded as an unavoidable concomitant of these processes. Even in coking processes, where the production of large amounts of coke has been accepted, the principal objective has been to maximize the yield of high value liquid products and to minimize the coke make, especially of the lower value shot coke. There has therefore been a continuing need to reduce the coking tendencies of petroleum feedstocks.
Various apparatus and process configurations have been employed to minimize coke yield, for example, as described in U.S. Pat. No. 4,385,985 and other approaches have attempted to improve the stability of the feedstock, for example, as described in U.S. Pat. No. 3,331,769, where treatment with a metal compound is used to reduce the degree of coking during a hydrotreating step. Other processes for upgrading and improving the stability of petroleum liquids are described in U.S. Pat. Nos. 3,839,187, 4,181,597 and 4,329,221.
Although the use of hydrogen donors may be effective to remove contaminants without causing a significant degree of coking, as described in U.S. Pat. No. 3,839,187, it would be desirable to avoid the use of hydrogen or hydrogen donors and to rely instead, upon a simple non-hydrogenative process.